1. Field of the Invention
The present invention relates to a light pointing device employed in an input apparatus, driving method and an input apparatus using the same, and more particularly, to a light pointing device employed in the display panel with a input sensing function and a method of driving the light pointing device to generate flashing light.
2. Description of the Related Art
Liquid crystal display panels have been widely utilized as the display devices of electronic appliances in recent years, for instance mobile phones, personal digital assistants (PDA), notebook computers and tablet computers. The liquid crystal display comprises an array substrate and a driving circuit. A plurality of pixels are disposed at the intersections of scan lines and signal lines on the substrate. Furthermore, the driving circuit drives the scan lines and the signal lines.
In another aspect, input-type display, such as a touch-type display, etc., is the optimum solution for products that require a user-friendly design. In particular, input and output interfaces are integrated with a display (monitor); such integration cannot, be achieved by traditional input apparatus. Traditional display devices can accept input commands from a finger or a touch control pen, and have additional sensors or a sensing film disposed on the screen. Therefore, the cost is increased, and the optical performance is affected. Recently, there have been proposed techniques that integrate the sensor array of amorphous silicon thin film transistors (a-Si TFTs) into the array substrate of an a-Si TFT-LCD. Furthermore, photosensitive sensors are individually embedded into specific pixels of the display. This, type of LCD panel is also called an in-cell touch panel.
Sensors used today are classified into two kinds, an electric charge type (also known as a capacitive type) and a current type (or resistive type). FIG. 1 is a circuit diagram of a capacitive sensor. The capacitive sensor 10 comprises a readout TFT 11, a photosensitive TFT 12, and a storage capacitor 13. The photosensitive TFT 12 will discharge the storage capacitor 13 when the photosensitive TFT 12 is exposed to sufficient light. When the next frame is displayed, a gate signal applied to a scan line 15 will turn on the readout TFT 11, and the storage capacitor 13 will be recharged again and detect the amount of electric charge by the read line 14. Furthermore, Vbias shown, in FIG. 1 represents a bias voltage.
Referring to FIG. 2, a resistive sensor 20 has no storage capacitor to store electric charges. After the photosensitive TFT 22 senses light, current will pass through the readout TFT 21. At the same time, the readout TFT 21 is turned on by a gate signal applied to the scan line 25. Simultaneously, the read line 24 will be used to detect the amperage of the current passing through. For both the capacitive type and resistive type of sensors, the a-Si TFT is subjected to light to cause an increase in channel carriers, and therefore raises the current level passing through. Basically, the variances in the photocurrent level are used as the sensed signal.
Alternatively, based on operating modes, the embedded touch panel can also be classified into a shadow type or an excess light type. The former directly compares the light, intensity between its environment and where light is shadowed by the finger, thereby achieving the touch pointing, function. However this operating mode will be affected when the light intensity from the environment is too low. That is, the contrast between the obscure environment and where light is shadowed by the finger is decreased so that the touch panel cannot recognize the actual input location pointed to by the user. The latter operating mode (excess light) can solve this problem by pairing with an auxiliary light source or a light pen, and ensuring proper operation under any environment.
For touch panels used by mobile appliances, the excess light operating mode using the light pen is the better choice. However, power consumption of the light pen is an issue that will affect its workable period in mobile use. Therefore, how to design a light pen that, saves much power becomes an important topic.